Multiple Fibres: Beyond the diffusion tensor

This chapter covers techniques for resolving multiple fibre populations in each voxel, as well as methods to exploit the information they recover. It begins by describing the limitations of DTI and the problems that complex white-matter configurations such as crossing fibre-populations and bending fibres present. It then goes on to describe multiple-tensor models, diffusion spectrum imaging, QBall, spherical deconvolution and persistent angular structure (PAS) MRI, along with a summary of pros and cons of each method. The next section covers useful information that can be extracted from the output of the techniques presented, such as estimates of fibre-orientations and indices of anisotropy and complexity. Finally, tractography methods for exploiting the multiple-fibre reconstruction algorithms and their metrics are briefly discussed.